$-kl - 9l + m + 4 = -2l - 7m + 2$ Solve for $k$.
Explanation: Combine constant terms on the right. $-kl - 9l + m + {4} = -2l - 7m + {2}$ $-kl - 9l + m = -2l - 7m - {2}$ Combine $m$ terms on the right. $-kl - 9l + {m} = -2l - {7m} - 2$ $-kl - 9l = -2l - {8m} - 2$ Combine $l$ terms on the right. $-kl - {9l} = -{2l} - 8m - 2$ $-kl = {7l} - 8m - 2$ Isolate $k$ $-k{l} = 7l - 8m - 2$ $k = \dfrac{ 7l - 8m - 2 }{ -{l} }$ Swap the signs so the denominator isn't negative. $k = \dfrac{ -{7}l + {8}m + {2} }{ {l} }$